Production of casts generally involves making a casting mold having a cavity (and, if necessary, a core) of casting sand, forming a pouring cup, a sprue, a runner and a gate to make a passage leading to the cavity through which molten metal is fed to the cavity (these elements will hereinafter be referred to inclusively as a gating system), and additionally forming a vent, a feeder, and a flow-off which lead to the outside. The gating system, vent, feeder, and flow-off are formed integrally with the casting mold, or the gating system is assembled from elements made of refractories such as earthenware and brick.
Where a casting mold, a gating system, etc. are integrally formed of casting sand, it is difficult to design the gating system in a three-dimensional and complicated configuration. Moreover, sand must be prevented from entering molten metal. Where, on the other hand, elements made of refractories are used to form the gating system, it is necessary to prevent molten metal temperature drop due to heat loss, and the assembly of the elements is troublesome, involving joining refractory elements by tape winding. In addition, after casting, the refractories break due to thermal shock, etc. to produce a large quantity of industrial waste, the disposal of which is labor intensive. In cutting refractory to length, a high-speed cutter such as a diamond cutter must be used. In general, refractories are hard to handle.
The technique disclosed in JP-A-U-1-60742 (Japanese utility model laid-open publication) is among known methods addressing these problems. According to this technique, a heat-insulating material obtained by molding a slurry comprising organic or inorganic fiber and an organic or inorganic binder in a mold is used in a gating system, etc.
Since the heat-insulating material is molded from a mixture of organic or inorganic fiber and an organic or inorganic binder, (1) where an organic fiber and an organic binder are combined, the heat-insulating material thermally decomposes on molten metal feeding to cause the gating system to shrink largely, which can lead to molten metal leakage from the gating system. (2) Where an inorganic fiber and an inorganic binder are combined, it is difficult to mold into a heat-insulating material in a three-dimensional configuration (e.g., a hollow shape) or in a design with a joint, resulting in a failure to make a gating system, etc. matching various cavity shapes.
It is also known to use a core produced from cellulose fiber mixed with inorganic powder and/or inorganic fiber (see, e.g., JP-A-9-253792). Containing inorganic powder or inorganic fiber, the core can be produced with suppressed shrinkage on drying. By use of this core, generation of gas or tar-like polymers from cellulose fiber during casting can be suppressed. As a result, casting defects are reduced, and casting workability is improved.
Notwithstanding these advantages, the core according to this technique contains no binder. Therefore, it is not suited to assemble a gating system and the like including a hollow runner in conformity to various cavity shapes.
Accordingly an object of the present invention is to provide an element made by papermaking technique for use in the production of casts which is less liable to thermal shrinkage accompanying thermal decomposition, capable of assembling a gating system, etc. in conformity with various cavity shapes, and is easy to handle.